Storage tank for oils and other liquids



July 9, 1946.

w. G. LAIRD STORAGE TANK FOR OILS AND OTHER LIQUIDS Original Filed April16; 1940 INVENIOR WILBUR 6. LAIRD- Patented July 9, 1946 OFFICE STORAGETANK FOR OILS AND OTHER LIQUIDS Wilbur G. Laird, Pleasantville, N. Y.

Continuation of application Serial No. 329,875, April 16, 1940. Thisapplication May 1, 1943,

- Serial No. 485,310

2 Claims.

This invention relates to improvements in apparatus for storing orholding volatile liquids, and more particularly to improvements in meansfor controlling the operation of floating decks in tanks to prevent suchdecks from tipping and upsetting and then sinking.

This application is a continuation of pending application Serial No.329,875, filed April 16, 1940.

Various types of floating roofs, covers or decks have been used in oilstorage tanks for reducing the evaporation of the volatile components ofthe oil, but considerable diflicult and loss has been caused by thesinking and destruction of such decks. Since these decks are normallysupported at all points by the oil on which they float, relatively thinsheet steel is employed in their construction. Under usual conditions nogreat safety factor is necessary to insure rigidity of the structure,but the formation of ice, collection of snow,

dust and dirt on one side of a deck is sufficient to cause a deck to tipor tilt, fill with oil and sink. Sometimes one side of the deck willstick to the side of the tank, because of ice or other causes, and sink,with serious consequences.

In the construction of oil tanks of the type illustrated, it iscustomary to make the rigid portion of the deck considerably smaller indiameter than the normal diameter of the tank. Any slight unequalsettlement of the foundation tends to throw the tank out of round, andwind pressure frequently has the same effect. Furthermore, it iscustomary practice to lap the sheets to form the circumferential seamswith the sheet above inside the sheet below, making the top of the tanksomewhat smaller in diameter than the bottom. For these and otherreasons the diameter of the rigid portion of the deck may be 18" or soless than the diameter of the tank itself; smaller clearance may be usedfor smaller tanks. The unequal or varying clearances resulting fromthese conditions makes it impracticable to utilize they areveryexpensive and difficult to make and keep air and liquid-tight.

The primary object of the presentinvention is therefore to provide other.and .less expensive means for preventingthe tipping andupsetting offloating decks in liquid storage tanks, in which the decks are entirelysupported by the liquid.

Another object of the invention is to provide positive means for keepingfloating decks in a substantially horizontal position on the liquid onwhich they float, While at the same time allowing such decks to movefreely up and down with the level of the liquid.

Accordingly, the improvements of the present invention for preventingthe tipping of a floating deck in a storage or other tank for liquidscomprise a cable or a plurality of flexible substantially taut metalcables attached to the deck and tank at distributed positions with theends or selected portion of each cable fixed at predetermined points andwith other portions of each cable held in movable relation to the otherpoints by means of sheaves which are fixed to the apparatus at saidother points and on which portions of such cable moves, each cable beingattached to said deck at two substantially spaced points and arranged toprevent one of said last mentioned points from changing its verticalposition in at least one direction with respect to the other point.

The present invention is based on the Wellknown principle of securingparallel motion by means of rope or other flexible lines arranged totransmit simultaneous and concordant motion to two or more points orparts of an apparatus. The principle has been applied to drawing boardinstruments and by Pease and Gadd in 1890 to water-sealed bell gasholders, Patent Nos. 435,186 and 433,463. Some 42 years'later Peaseagain applied the principle to the piston of a dry gas holder (PatentNo. 2,050,459). This Was about two years after applicant had applied itto the same purpose (Patent No. 1,894,535). This invention makes use ofthe principle in connection with metal cables to prevent the tipping offlat decks which normally float on the liquid in oil storage tanks andthe like.

The present invention includes other features and details of thearrangement and functioning of the cables as will be apparent from thefollowing description thereof taken in connection with the accompanyingdrawing forming a part of this application.

In the drawing:

Fig. 1 is a vertical cross-sectional View of an apparatus for storing orholding liquids in which one form of the present invention isillustrated.

Figs. 2 and 3 are views similar to Fig. 1 showing modified forms of theinvention,

, Figs. 4, 5 and 6 are broken vertical sectional views of liquid storageapparatus on a smaller scale than those shown in Figs. 1 to 3, andillustrating further modifications of the apparatus of the presentinvention.

While the improvements of the present invention may be applied tofloating decks or covers in tanks for storing or holding variousliquids, the improvements have particular application and will bedescribed and illustrated in connection with oil storage tanks.

Referring to Fig. 1 of the drawing, the oil storage apparatusillustrated therein comprises a cy lindrical steel tank of usualconstruction including a sheet steel bottom l0 and a sheet steel sidewall l2. The apparatus also includes a floating deck I4 of smallerdiameter than the tank and which may be of any type of construction, butwhich, as shown, comprises a pan-like structure having an outside rim orflang extending substantially above the liquid in the tank. The bottomof the deck slopes down toward the center to prevent vapor and gas frombeing trapped, and for drainage purposes. The deck may be provided withthe usual jointed rain water drainage pipe l6 which takes the water fromthe deck and delivers it to any desirable point, for example, some pointoutside the tank. A water sealed trap to discharge the water directlyinto the tank may be used in place of the line it. And any suitable lineor swing-line may be used to supply oil to and draw oil from the tank.

In Fig. 1 the improved arrangement for we venting the deck M fromtipping and upsetting in the tank, comprises a set of similar cables l8arranged so that some cables apply opposing stresses to certain pointson the deck from those applied by other cables of the set. The cables [8each have one end fixed to an elevated part of the tank or otherstationary part of the storage apparatus, for example, by means of abracket 28. From that point each of the cables 18 passes under a sheave22 and over a sheave 24 mounted in fixed position on substantiallyspaced or opposite portions of the deck l4, and then extends downwardlysubstantially on the opposite side of the deck, from the bracket 2! tothe lower portion of the tank where its other end is fixed to the tankby a lug' or other means as shown.

It will be noted that, as shown in Fig. 1, each cable [3 is mounted in asubstantially opposite manner to another cable [8 of the set so that thedeck must move, if at all, ma horizontal plane which is its normalfloating position. This is apparent because, if th right side of thedeck i4 is bound on the side of the tank, with ice for example, the endof the cable 18 on the left side will hold up the left side of the deck,which can not go down without receiving cable slack from the right sideof the deck over the sheave 24. The cables have the same constrainingaction on the deck if the sheaves are fixed in inverted position on thebottom edge of the deck as in Fig. 5.

In Fig, 2 the deck [4 is held in horizontal position and kept fromtipping by means of substantially taut cables 26, both ends of each ofwhich are fixed to the deck. Each cable 26 has one end attached to oneside or edge part of the deck, for example, at a point 28, and fromthere passes in succession over sheaves 3U, 32, and 34, which are fixedto the tank or other part of the storage apparatus in approximately therelative positions shown, and thecther end of the cable is fixed tothe'opposite side or a remote edge portion of the deck [4 at a point 36.As shown in this figure, the cables may be regarded as mountedsubstantiall in pairs, so that the ends of one cable of the pair act onsubstantially the opposite sides of the deck to that of correspondingends of the other cable of the pair. The adiacent points 28 and 36 neednot be in exact vertical alignment. A. pair of cables mountedsubstantially oppositely, as shown, prevents one side of the deck fromchanging its vertical position with respect to the other side of thedeck, if unevenly loaded with snow, ice, etc. A single cable may takethe place of two cables 26, as shown in opposed mountings, by making thefixed points 23 and 36 coincide, or by using an endless cable fixed tothe deck at two points such as 28 or 36, but which has the length andmounting of two opposing cables 26.

In Fig. 3, the deck I4 is controlled by a plurality of cables 32distributed around the tank and deck. One end of each of these cables 38is fixed with respect to the point 40, at the top of the tank, and fromthere is mounted around sheaves 52 and 34 set in fixed position,respectively on the outer edge of the bottom of the deck l4 and on thebottom of the deck near its center or at a point a substantial distancefrom the edge of the deck. From the sheave 44, the other end of eachcable is fixed at a point 46 directly below the sheave M. In thisfigure, it will be noted that the deck [4 at the points of the sheaves42 cannot be lowered without pulling the cable over the sheaves 44, andthereby also lowering the center of the deck. Since some decks of thistype are substantially rigid in View of the vertical outside rim and thedownwardly sloping bottom, it is apparent that the cable arrangementshown in Fig. 3 will cause the deck as a whole to move upwardly ordownwardly in substantially horizontal position with the upward ordownward movement of any one side of the deck. For large tanks thesheaves 44 may actually be nearer the edge of the deck than the center.

The cable arrangement shown in Fig. 4 is a modification of that shown inFig. 2, in which a cable 48 has one end fixed to the edge of the deck l4from which it passes in succession over sheaves 50, 52 and 54 insubstantially the relative positions shown, and then has its other endfixed to some point of the deck 56, which is substantially removed fromthe point of attachment of the other end of the cable 48, but which maybe on the edge, middle or, any other desired point on the deck. Thepoint 56' corresponds to the point 36 in Fig. 2 which is on the oppositeend of a cord or diameter from the point 28. It is apparent that in theapparatus shown in Fig. 4, with a sufficient number of cables 48distributed around the deck; for example, three or more cablesdistributed uniformly; one portion of the deck cannot move in a downwarddirection or sink in the oil without pulling the other portion of thedeck down also. Unless the point 56, for

" example, moves downwardly, it is clearly impossible for the left sideof the deck to go down.v

Fig. 5 shows a modification of the cable arrangement in which a numberof distributed cables such as the cable 58 have their ends fixed 70' Jthere is mounted over sheaves 62 and B4 respec- 'tively at one edge of-adeck l5, and at some pre- '5 determined point which may be near thecenter of the deck. In this instance, the other, end of the cable 58 isfixed to the top of a post or pillar 166 which extends from the bottomof the tank through an opening 68 in the deck. In the apparatus showninFig. 5, it is apparent that the portion of the deck around the pillar.66 cannot move downwardly without at the same time drawing the cableover the sheave 62 and pulling the left edge of the deck; down. Thesheaves 62 and 64 may be mounted on the top of the deck as in Fig. 1, ifdesired.

It is to be understood that in Fig. anynumber of cables 58 may beused,-and that in any case at least three cables regularly positionedshouldbe used. Any number of posts or pillars 66 may be used in a tank,

The modification shown in Fig. 6 is a further variation of the formdescribed in connection with Fig. 2, in which a single cable mounted inan endless or series arrangement is used as a safety device for anentire deck. In this figure a continuous cable 10 is mounted insubstantially taut condition over a series of regularly spaced groups ofsheaves 12, 14 and 16 fixed in the relative positions shown. The cableis clamped or otherwise fixed to the deck at the position of each groupof sheaves by means of a series of clamps 18. A deck should have atleast three points of attachment 18, to the cable 10; very large tanksmay require from 6 to 10 or more for proper protection, depending uponconditions. With the arrangement shown in Fig. 6, all points 1.8 mustmove in the same direction at the same time, re-

gardless of a greater load of dirt, etc., on one side.

While individual cables or sets of cables may be mounted in still otherways, all arrangements come within the two general species in which thecable is either fixedwith respect to the tank or with respect to thefloating deck." The upper and lower sheave mountings (Figs. 2 and 6) maybe reversed if desired, but relatively long spans ,of cable are not sodesirable above or at the top of the tank.

If the upper and lower cable mountings are reversed, with the cablesfixed to the deck, as in Figs. 2 and 6, the cables may be mountedoutside the tank with the use of additional sheaves. For example, acable such as 26 may be fixed to the deck at 36, pass around a sheave atthe bottom of the tank, then over a sheave directly above on top of thetank, down on the outside of the tank to the bottom, over a sheave, thenunder the tank to the opposite side, over a sheave, up to the top of thetank, over a sheave, and then down to the deck at 28 where the cable isfastened.

In general, a deck should be provided with at least three points ofcable engagement. Some of the larger tanks require more for properprotection. Cables of corrosion resistant metals or alloys may be usedfor particular purposes, and in any case an old or corroded cable may bereadily replaced by threading it over the sheaves as the old one ispulled out.- Cables indicated as fixed to the bottom of the deck or tankas shown in some of the figures of the drawing are preferably passedover a sheave at the point of attachment and the end of the cableactually fixed to the upper part of the tank or deck structure so thatcable replacement will be easy.

The term cable as used in the specification and claims is understood toinclude any type of flexible line suitable for the purpose, metal orwire rope, chain, strap or rod, used in whole or in part, in accordancewith the invention, to effect the restraining" or stabilizingarrangements for holding a floating deck in horizontal position on aliquid on which it is adapted to float. Hemp rope may beused in any casewhere suitable or desirable.

Flexible line ortcable may be employed for movement over the sheaveswhile metal rods, straps, chains or other suitable material may beused'for theother portions of the restraining or stabilizing means.

Pan-type decksilike the deck I4 are used to reduce vaporization bycovering most of the surface of the liquid in the tank, and any gas orvapor formed beneath the deck is preferably allowed to escape around theoutside of the deck. The deck must" be free tomove horizontally toavoidirregularities in the effective tank diameter and wall surface.vHowever, the space between the deck and tank may be covered if desired,by some flexible or variable covering to reduce evaporation losses andto keep out as much rain, dust and dirt as possible.

The cable or cables may be applied to any type of floating deck (pan orcovered), cover or other floating buoyant element in a tank containing,

or for holding, or storing, liquids of any kind,

regardless of the purpose for which the floating deck or buoyant elementis employed. It is to be understood thatthe termfdeck as used in thisapplication includes any form of floating cover or element, unlessotherwise limited in the claims.

The cable or rope arrangements of the present invention which merely actas safety devices are well suited to the purpose of preventing floatingdecks from tipping and being caused to sink in the liquidon'whichthey'float,'because the normal movements of such decks, up and down andhorizontally, are. not interfered with. (The cables prevent'appreciablerotation of the deck in the tank.) Furthermore, a floating deck equippedwith cables as described may be safely Walked upon by a repair man,inspector or gauger. In fact, "any unequal loading which may resultfromrain, leakage, snow, ice, sleet, dirt, etc., is carried on the deckas an unbalanced load by the cable or cables which take the strain.

Under normal operating conditions, the deck, which is slightly smallerthan the inside diameter of the tank, floats on the liquid in the tank,and except for abnormal influences, is kept in a substantiallyhorizontal position by the liquid,

' which, unlike a gas, naturally resists deformation of its levelsurface. The cable arrangements of this invention are installed toprotect the deck from the unusual circumstances mentioned, since tanksof this type are large and open to the atmosphere, and are subject toabnormal weather, corrosion, etc. Without the cable safety means, thedeck, if unequally loaded for example, may be depressed at one edgebelow the surface of the liquid and caused-to sink. And when anunprotected deck sinks under these conditions, it is almost alwayscrumpled up and destroyed, because of its relatively light constructionand because it goes down at a steep angle.

If a deck equipped with the cable arrangement of the present inventionshould be caused to sink because of leakage or other unavoidablecircumstances, the deck as a whole will settle slowly in horizontalposition so that it will not be damaged, but will come to rest upon thesupporting structure, not shown, which is used in floating deck liquidstorage tanks, so that it may be cleaned or repaired when the tank isemptied. A tank is to be understood as including any type of storagevessel or reservoir for liquids in which one or more floating decks ordeck units are or may be used.

Having described the invention in its preferred form, What is claimed asnew is:

1. An apparatus for holding liquids which comprises an uprightopen-topped cylindrical tank capable of withstanding the hydrostatichead of liquid stored therein, a buoyant floatable sheet metal deckwithin said tank adapted to be floated by the liquid in the tank in asubstantially horizontal position under normal conditions, said deckbeing of sufficient area to substantially cover the liquid in the tankbut of sufficiently smaller diameter than that of the tank to leave anarrow annular space between the outside edge of the deck and the insideof the tank wall in which liquid displaced by the deck may rise freelyand by which vapor evolved from the liquid in the tank may escape, thesaid deck having an outside rim extending substantially above the normallevel of the liquid in said annular space when said deck is floating,said deck being normally freely movable vertically in the tank, andsafety means for restraining said deck from any substantial tipping fromits normal substantially horizontal floating position on the liquid inthe tank which may be caused by ice formation, unequal loading of thedeck by snow, sleet, dirt, leakage and other abnormal causes, said meanscomprising flexible cable stabilizing means mounted at distributedpositions around said deck and tank with selected cable portions fixedat predetermined points and with other cable portions held in movablerelation to other points by means of sheaves attached to the apparatusat said other points and on which portions of cable move, a cableportion associated with each of said distributed positions beingattached to said deck at two substantially spaced points and arranged toprevent one of said last-mentioned points from substantially changingits vertical position with respect to the other of said last-mentionedpoints; said flexible cable stabilizing means being arranged in such away as to permit the free normal vertical and sidewise movement of thedeck on the liquid on which it floats.

2. An apparatus for holding liquids, which comprises an uprightopen-topped cylindrical tank capable of withstanding the hydrostatichead of liquid stored therein, a buoyant floatable sheet metal deckwithin said tank adapted to be floated by the liquid in the tank in asubstantially horizontal position under normal conditions, said deckbeing of sufiicient area to substantially cover the liquid in the tankbut of sufflciently smaller diameter than that of the tank to leave anarrow annular space between the outside edge of the deck and the insideof the tank wall in which liquid displaced by the deck may rise freelyand by which vapor evolved from the liquid in the tank may escape, thesaid deck having an outside rim extending substantially above the normallevel of the liquid in said annular space when said deck is floating,said deck being normally freely movable vertically in the tank, andsafety means for protecting said deck from any substantial tipping fromits normal substantially horizontal floating position on the liquid inthe tank which may be caused by ice formation, unequal loading of thedeck by snow, sleet,

dirt, leakage and other abnormal causes, said means comprising flexiblecable safety means mounted at distributed positions around said tank anddeck, parts of the cable at each position being fixed to the apparatusat predetermined points of attachment and other portions of the cable ateach position being held at other points of attachment to the apparatusby at least two sheaves on the intermediate portion of such cable whichare fixed to said apparatus at said other points, said points ofattachment to the apparatus including the attachment of the cable ateach position to said deck at two substantially spaced points which arein substantially vertical alignment with points of attachment to fixedparts of the apparatus, said cable safety means being distributed andarranged around said deck and tank and the cable at each position beingattached to the apparatus in such a way as to allow movement of the deckvertically and horizontally on the liquid on which it floats and toprevent the deck from tipping substantially from its normal floatingposition on the liquid.

WILBUR G. LAIRD.

